Need help with PS action keyboard assignements

I'm in the process of developing a new action template and I have run across several combinations that will not let me assign an action to it. However, when I look through all the actions, none has used up those spots. I tried one of them, Ctrl-F4 and it attempts to close the file I'm working with.

Is there some way to disable that keyboard action so that I can re-use it for something else? I don't even know where to look to do that because it's not listed on my actions pallette as an action. Thanks for your help!